1. Field of the Invention
The present invention pertains to a machine for inserting a cathode in a cathode tube gun.
2. Description of the Prior Art
Machines currently used to insert electron gun cathodes for cathode tubes measure the distance between the active side of these cathodes and the grid 1 (or the grid 2 as the case may be) with complicated, slow instruments which have difficulty in maintaining necessary precision.
For these machines position the cathode with respect to the grid 1 by first interposing a sensor of a fixed length between the cathode and the grid 1. The cathode is placed on a fixed support and the gun is placed on a movable support driven by a wheel which works with a cam-shaped groove of a leading screw which is itself driven by a stepping motor.
A first stopping stage of this groove determines the measuring position and position-setting of the cathode. Then the gun is drawn back, the sensor is released and the gun is brought forward by a distance equal to the distance by which it has been moved back plus the length of the sensor, and reaches the position where the cathode is soldered to the gun eyelet. This position too is determined by a stopping stage of the groove. Thus any modification in the setting of the machine means that the sensor has to be dismantled and machined to new dimensions. The device for driving the leading screw and the wheel is not precise: for example, the groove of the leading screw should be free of dust and debris but this is difficult to achieve in a factory environment. Even if the stepping motor stops precisely in the desired angular position, the device for coupling with the leading screw, that it drives, has backlash which is difficult to take into account. The forces exerted on the wheel, both by the gun carriage and the leading screw, cause the backlash in this transmission of motion to be reflected at the carriage. Furthermore, if the cathode eyelet is out of axis, the sensor may deform the eyelet unless the sensor itself is made of a deformable material.
An object of the present invention is a fast, precise and reliable method to insert a cathode in a cathode tube gun, where the rod of the sensor does not have to be deformable but yet in no way deforms the eyelet of the cathode.